96 Mr. Gilbert on the Nature 



made wide, and so constructed as to allow of the whole breadth 

 bearhig at once ; and every portion in contact with the ground 

 should roll on it without the least dragging or slide : but, it is 

 evident from the well-known properties of the cycloid, that the 

 above conditions cannot unite unless the roads are perfectly hard, 

 smooth, and flat ; and, unless the fellies of the wheels, widi their 

 tires, are accurately portions of a cylinder. These forms, there- 

 fore, of roads and of wheels are the models towards which they 

 should always approximate. 



Roads were heretofore made with a transverse curvature to 

 throw off water, and in that case it seems evident that the peri- 

 pheries of the wheels should in their transverse sections become 

 tangents to this curve, from whence arose the necessity for dishing 

 wheels, and for bending the axes; which contrivances gave some 

 incidental advantage for turning, for protecting the nave, and by 

 affording room for increased stowage above. But recent experience 

 having proved that the curved form of roads is wholly inadequate 

 for obtaining the end proposed, since the smallest rut intercepts 

 the lateral flow of the water; and, that the barrel-shape conBnes 

 carriages to the middle of the way, and thereby occasions these 

 very ruts, — roads are now laid flat, carriages drive indifferently 

 over every part, the wear is uniform, and not even the appearance 

 of a longitudinal furrow is to be seen. It may, therefore, con- 

 fidentially be hoped that wheels approaching to the cylindrical 

 form will soon find their way into general use. 



The line of traction is mechanically best disposed when it lies 

 exactly parallel to the direction of motion, and its power is dimi- 

 nished at any inclination of that line in the proportions of the 

 cosine of the angle to radius. When obstacles frequently occur, 

 it had better perhaps receive a small inclination upwards, for the 

 purpose of acting with most advantage when those are to be over- 

 come. But it is probable that different animals exert their 

 strengths most advantageously in different directions, and there- 

 fore practice alone can determine what precise inclination of this 

 line is best adapted to horses, and what to oxen. These consi- 

 derations are, however, only applicable to cattle drawing imme- 



